1. Field of the Invention
The present invention relates to a photographic camera and more particularly to a data exposure device which is adapted for recording on a photographic film shooting data together with a picture on the film.
2. Description of the Prior Art
A data recording device is used, for example, in cameras, for the purpose of exposing photographic film in the camera to light images which indicate shooting data such as the date and time of the shot, aperture value, shutter speed, and so forth. Amongst various types of data recording device, a device known as "data back" is adapted to be fitted on the rear of a camera, after removing the rear cover of the camera. This type of data recording device has a light source means such as lamps or LEDs which are adapted to be lit to form a light image of the shooting data in response to a signal from a camera, e.g., a shutter release start signal, a front curtain travel completion signal or an exposure completion signal.
The duration of lighting of the data image light source is determined beforehand in a control circuit to effect optimum exposure on the photographic film, taking into account various factors such as the sensitivity of the film.
Usually, due to the small lighting power of the light source, the lighting time is considerably longer than the shooting exposure time for picture taking. This causes a problem when the camera is operated for continuous shooting by a motor drive unit which is arranged to drive the camera wind-up system in response to an exposure completion signal derived in the camera. Thus, when the camera is equipped both with a data back and a motor drive for continuous shooting, there is a possibility that the motor drive unit may wind up the camera and advance the film before the data recording is completed. If the film is advanced during the data recording, the data image being recorded on the film will be moved undesirably. This problem is serious and continuous shooting is substantially impossible particularly when the film has a low or slow sensitivity because such a film requires a longer time for the data light exposure.
In order to overcome this problem, a camera has been proposed in which both a winding start signal and a data recording trigger signal are produced upon completion of the exposure and, at the same time, a winding prohibition signal is given to the motor drive unit until the data recording is completed. The motor drive unit starts the camera wind-up only after the winding prohibition signal is cancelled following completion of the data recording.
This camera, however, encounters a problem in that the camera cannot perform high-speed continuous shooting when the data recording device is used, because it operates in such a sequence that winding is possible only after the data recording is completed.
In order to enable a camera with data exposure function to perform high-speed continuous shot, U.S. Pat. No. 4,470,677 proposes a data exposure device which is adapted for effecting data exposure only on the first frame of the continuous frames of the film in each continuous shot.
This data exposure device, however, has problems due to the fact that the high-speed continuous shooting is usually conducted for a specific purpose in which a regular time interval between successive frames is essential, as in the case of sports photography or scientific photography. Namely, in the case of the above-mentioned U.S. Pat. No. 4,470,677, the timing of shutter release for the second frame must be delayed due to the necessity of sufficient time for the data to be recorded on the first frame. In consequence, the shutter release opportunity for the second frame may be lost and the time interval between the shots on the first and the second frame is longer than the time interval between other successive frames.